
Geometric sum
I'm having a bit of a mental lockup on a simple sumproblem, but perhaps someone here could just give a hint as to what I'm missing.
$\displaystyle x^n1 + x^{n2}y + x^{n3}y^2 +... + xy^{n2} + y^{n1}$
I'm not really new to sums and their formulaes, my real problem here is that I can't seem to get the quotient for the sum; it reverses so to speak:
$\displaystyle {x^{n2}y}/x^{n1}$ and $\displaystyle y^{n1}/xy^{n2}$
and I'm not sure what to do with that. I'm not after a complete solution, just a hint or two so I can figure it out!